Arbekacin (free base) is a compound having the following structure, and a sulfate thereof is used for the treatment of pneumonia and sepsis caused by methicillin-resistant Staphylococcus aureus.

A general method for arbekacin sulfate normally uses arbekacin free base synthesized by a method described in Japanese Examined Patent Application Publication No. Sho 52-33629 (PTL 1) or the like, and includes adding sulfuric acid to an aqueous solution of the arbekacin free base, followed by freeze-drying to obtain the arbekacin sulfate in a solid form. In this case, the synthesized arbekacin free base is purified by chromatography. However, this method is not efficient because improving the purity generally requires a large amount of a resin, requires related substances to be removed by changing the eluent concentration stepwise, requires a large amount of the eluent, requires a long time to carry out the procedure, and requires other things. In addition, the arbekacin sulfate obtained by this method unavoidably contains approximately 1 to 2% of related substances such as dibekacin.
Arbekacin can also be used as arbekacin free base without being converted into a pharmaceutically acceptable salt such as a sulfate. Moreover, it is also possible to convert arbekacin free base to pharmaceutically acceptable salts other than sulfate for use. Nevertheless, arbekacin free base is likely to degrade, particularly, degrade at position 1′″, so that dibekacin is formed as illustrated in the following equation. For this reason, arbekacin free base needs to be stored at low temperature, which is industrially disadvantageous.

Note that Japanese Examined Patent Application Publication No. Sho 63-32799 (PTL 2) and The Journal of Antibiotics, vol. 26, 1973, p. 412 (NPL 1) state that the crude arbekacin free base obtained by reactions is purified by chromatography and concentrated to dryness to thus obtain arbekacin dicarbonate. However, in these methods, arbekacin carbonate is unintentionally formed during concentration of the solution resulting from purification of arbekacin free base by chromatography. And this arbekacin dicarbonate is obtained by drying without performing a purification step. Hence, the methods do not include intentionally forming arbekacin carbonate and purifying it by isolation. Furthermore, these literatures do not disclose carbamic acid of arbekacin or arbekacin derivatives.